1. Field of the Invention
The invention relates to work over vessels in general and jack-up work over vessels in particular.
2. Prior Art
Oil and gas wells must be serviced occasionally for a number of reasons. For example, valves or seals may need to be replaced; flanges may need to be removed or installed in the wellhead; and blowout preventers may need to be removed, added, or serviced. The well may need production treatment, such as fracturing or acidizing, to stimulate the production of oil or gas therefrom. During treatment, the wellhead may need to be removed for well stimulating chemicals to be injected into the well. The packers and anchors in the well may need to be removed or reseated. Production tubing and well line tools may need to be removed from or run into the well. All of the foregoing are typically done with a workover rig.
Workover rigs typically comprise a derrick and pulleys or block and tackle devices that are used to extract the above described devices and related hardware from the well or to insert the same into the well. Although a workover rig has many functions, one of its principle purposes is to exert a vertical lifting force on the components in the well. In land based wells, this is simple enough. The workover rig is brought to well, and placed directly over the well, either with a mobile workover rig that can be rolled into the proper position or with a crane or other similar lifting device.
In offshore wells, proper placement of the workover rig is more difficult. The workover rig must be brought to the platform, usually on a barge powered by a tugboat. A separate vessel having a crane is then used to lift the workover rig onto to the drilling platform and position the same over the well. A platform may have many different wells originating therefrom. The crane will need to move the workover rig into position over each well so that each may be serviced. Once the well servicing is complete, the crane will return the workover unit to the barge for return.
Typically, the workover rig, the barge and tugboat, and the secondary vessel with the crane are leased by the day. Thus, maintaining both of these vessels and their crews during workover can be quite expensive. Therefore, a vessel that can meet the following objectives is desired.